Boulder - Denver - Golden - Fort Collins - Lyons - Geology

Colorado's Front Range communities lie where the Great Plains abruptly meet the Rocky Mountains. This geologically complex transition zone runs north - south throughout Colorado and physically divides the state. Cities like Ft. Collins, Boulder, Golden and Colorado Springs lie at the eastern base where elevations range 5,200' - 8,500'. The Front Range's granitic mountains came to be over billions of tumultuous years:

Geologic History:

The oldest rocks in the Front Range are carbon dated at 1.7 billion years old, or simply "Precambrian". The term Precambrian does not refer to an era, but rather a period 570M years ago considered the first geologic epoch of Earth. Precambrian rock consists of both metamorphic and granitic rock; metamorphic rock being older and generally found in the Boulder foothills.

Precambrian rock was buried deep and subjected to intense heat, pressure and chemical reactions that led to their present form. Schist, gneiss, and quartzite are the three most common types of metamorphic rock in the Colorado Front Range.

Once an ocean...

The Front Range was gradually flooded by a vast ocean around 600 million years ago at the beginning of the Paleozoic era.

In addition to marine deposits, sand and lime mud was deposited on beaches and buried under other sedimentary rock, eventually becoming sandstone and limestone. This area would subsequently flood and recede several times over the next 300 million years creating new, distinct strata each time.

The Ancestral Rockies formed around 300 million years ago when tectonic activity thrust 2 great mountain ranges in central and western Colorado up, exposing deeply buried Precambrian rock high above the surface. As Precambrian rock eroded, sediments were carried away, settled and compressed into sandstone and shale rock called the Fountain Formation.

Boulder's Flatirons and Sanitas Ridge are both part of the Fountain Formation.

Lyons Sandstone

Around 260 million years ago (the Permian period), waters receded and great sand dunes covered the area, shifting and essentially burying the original Fountain Formation.

The dunes, however, led to the creation of Lyons Sandstone. Well known for its pinkish hue, the Lyons Sandstone is commonly used in building construction and cannot be missed when driving through Lyons, Colorado. Layers of Lyons sandstone is exposed throughout Hall Ranch.

The Front Range was crossed by vast flood plains at the end of the Permian period. Rivers carried silt and sediment from the mountains down to the east, covering Lyons sandstone of the Permian period.

The sea returned from the north and south at the start of the Cretaceous period (140M years ago), beginning a cycle of advances and retreats over the next 100 million years.

Shale, coal, limestone and sandstone were the most common layers of sedimentary rock associated with this period. The ocean finally withdrew from Colorado at the end of the Cretaceous period.

There's Gold in them thar' hills

Around 70 million years ago in the late Cretaceous period, geologic forces triggered another round of mountain building.

Magma bubbled up through existing mountains and foothills to create bigger mountains and foothills. Sizzling magma heated mineralized water that seeped through cracks in the rock, leaving behind vast deposits of metallic ore. This was the beginning of Colorado's geologic gold rush.

As magma spewed to the Earth's surface from distant volcanoes, tectonic activity shaped the core of today's Front Range and Rocky Mountains.

Shifting ground and tectonic uplift tilted the Fountain Formation on its side. As the Fountain Formation broke through the Earth's surface, erosion shaped exposed rock into the iconic Boulder Flatirons.

During this time of mountain building and uplift, crushed rock and debris were once again brought down to the eastern plains by water. Hills and mesas across the Front Range were comprise these massive sedimentary deposits.

Today, the Front Range is experiencing a period of relative geologic calm. Volcanic activity is dormant, tectonic activity is virtually non-existent and in general, the geologic picture is stable.

Boulder - Denver - Golden - Fort Collins - Lyons - Wildlife

Colorado's Front Range lies where the Great Plains meet the Rocky Mountain uplift. Three distinct ecosystems with overlapping areas support a wide range of plants and animals in a relatively small space.

At least 18 amphibians, 48 reptiles, 123 mammals and 408 birds live in the Colorado Front Range at some point in their lifecycle.

Prairies of the high desert grassland steppe (5,000' - 5,500') are home to burrowing owls, badger, rabbit, rattlesnakes, ferruginous hawks and golden eagles.

Coniferous montane forests (7,000' - 8,500') are visited by elk, moose and even bighorn sheep on their annual winter migrations from the high country to more hospitable conditions at lower elevations.

Black Bear

Black bears come in a variety of colors including cinnamon brown, pale white and a bluish hue.

They do not have a hump, which makes them easy to discern from grizzlies. Black bear claws are also much darker and shorter than a grizzly's.

Black bears have color vision but poor eyesight, so they rely on a keen, directional sense of smell to navigate the wilderness and find food. They're opportunistically omnivorous, but primarily vegetarian.

Black bears do hibernate, but seldom sleep soundly through the entire winter. Bears occasionally wake up during hibernation and 'sleep walk' to find some food, drink water and go to the bathroom.

While not physiologically necessary, bears may wake during warm spells which falsely signal the onset of spring. Upon realizing that winter is still in full swing, bears will retreat to their dens. Hibernation may last 5-6 months depending on elevation, climate and available food.

Mountain Lion

Mountain Lions have the widest distribution of any native mammal in the Western Hemisphere.

Once hunted aggressively, populations have stabilized and are even moving east across the plains. Some models suggest mountains lions may reach east coast mountain ranges within the next 20 years.

Mountain lions are primarily nocturnal and sightings are infrequent, though certainly not rare. They prey mainly on deer and elk, but readily pursue birds, rabbits, porcupines and other small mammals when opportunities or conditions warrant.

On average, a mountain lion will consume one deer per week.

A mountain lion will cover the remains of its prey with brush, and return periodically to feed ("caching"). If you find a cache, leave the area immediately - there's almost certainly a hungry mountain lion in the vicinity.

Coyote

Coyotes are known for their adaptability and resilience, and accordingly are found throughout North America in variety of environments. Coyotes are carnivorous but not especially fickle: they feed on everything from small mammals, berries and grasses to the occasional left-over kill of another animal.

Coyotes are long distance runners, excellent jumpers and don't mind the water in pursuit of prey. They live in dens, which are usually located in hollow trees, burrows of another animal, caves or in dense brush.

Coyote pups are generally born in late spring and able to survive on their own by next fall. Coyotes are active both day and night.

A great way to distinguish canine and feline prints is by claw marks. If you see a print you are unsure about, look for claw marks. If you see them, more than likely the track was left by a canine. Felines have retractable claws and rarely show their claws in a track.

Golden Eagle

Unlike bald eagles of the Colorado Front Range, golden eagles are not true migrants. Because their diet consists of perennially available small to medium-size mammals, these eagles simply expand their home territory during winter.

Golden eagles tend to use the same nest site for many generations, employing pine boughs to enlarge or repair old nests. These scented boughs help control parasites by repelling insects that find the smell unappealing.

Females are generally larger than males; juveniles tend to be much darker than adults.

Peregrine Falcon

Peregrine Falcons range across North America but are uncommon in general.

Juveniles have darker underparts, and the black streaking is not quite as prominent.

Peregrines prefer ledges and cliff faces to nests in a tree. These inaccessible sites are known as eyries.

Due to successful habitat management and breeding programs, peregrine falcons were downgraded from "Endangered" to "Threatened" on the federal endangered species list in 1999.

Prairie Falcons look similar to peregrines, though its coloration is generally more pale. Rather than a stark black and white contrast, prairie falcons have gray spots on a much whiter underside.

Boulder - Denver - Golden - Fort Collins - Lyons - Ecology

Colorado's Front Range spans three distinct ecosystems with overlapping areas that support a wide range of plants in a relatively small space.

An estimated 700+ species of trees, shrubs, flowers and grasses inhabit Front Range Open Space and Mountain Parks; geology, elevation and climate heavily influence local populations and compositions.

Many of today's plant species evolved in the area, while others migrated here when the climate was quite different, or came recently by accidental or purposeful human introduction.

Native Front Range ecosystems include grasslands, high desert grassland steppes and montane forests, each interspersed with wetland and riparian sub-systems.

Grasslands (5,000' - 5,500')

Tall grass prairies once stretched east from the Rockies to Indiana, north to Canada and south through Texas. Only 2% of its original composition remains, much of it re-purposed by man or overtaken by mixed grass prairie.

Native short, mid and tall prairie grasses can still be found in protected areas across the Front Range, including bluestem, switchgrass, king spike fescue, western wheatgrass, prairie junegrass, sideoats grama, blue grama and buffalograss.

Intact foothills grasslands exist in small pockets along mountain-front areas. These include a mixture of mid-grasses on drier slopes, and tall grasses in wetter spaces.

Invasive weeds are a constant threat to native grassland habitat.

High Desert Grassland Steppe - Foothills (5,500' - 7,000')

As elevations increase near the foothills, open grasslands mix with ponderosa pine and pinyon-juniper woodlands.

Ponderosa pine not only survive such fires, but require it to open their cones for reproduction.

Fire suppression since the 1880s has created unsustainable forest densities that can result in destructive, high intensity fires. It's thought that only a few dozen trees once occupied an acre of land in the foothills, whereas today they can exceed thousands.

Foothills - Montane (6,000' - 8,500')

Coniferous trees dominate the upper Colorado foothills.

Primary constituents include pinyon pine, ponderosa pine and lodgepole pine. Douglas-fir, blue spruce, white fir and limber pine may be found in higher, western locations. Juniper is a ubiquitous member of the cedar family found from the grasslands to upper foothills.

Deciduous residents (trees that drop their leaves during winter) include aspen, Rocky Mountain maple, mountain ash, boxelder, cottonwood, willow, alder and birch. Most require proximity to water for survival.

The White Adder's Mouth Orchid, which grows wild on Green Mountain in Boulder, is not known to grow on any other site in Colorado. The Ute Ladies' Tresses Orchid is also quite rare in the western US, but found here.

Wood Lilies are listed as rare and imperiled by the Colorado Natural Heritage Program. Collecting has been a factor in this plant's decline. The vanishing Prairie Gentian wildflowers are protected on Front Range pastures. They occur in wet meadows east of Boulder, such as the Lower Boulder Creek Habitat Conservation Area.

Boulder - Denver - Golden - Fort Collins - Lyons - Contact

The Colorado Front Range is adminstered by multiple local, county, state and federal agencies. Each trail may be managed by one or multiple agencies. While specific contact information is listed on every trail page, the following is a list of contact information for the most popular areas.